Saint Angus the Culdee. Navigatio Sancti Brendani (Abbatis) (Voyage of Saint Brendan (the Abbot)). Tenth/mid-Eighth Century AD (AD 691/776):

“The Voyage of Saint Bredan” in O’Donoghue, Denis, tr. Brendaniana: Saint Brendan the Voyager in Story and Legend, pp104-178. Dublin: Browne & Nolan, 1893.
https://ia600905.us.archive.org/10/items/gb0U49kFVbJcsC/gb0U49kFVbJcsC.pdf

Mackley, J S. The Legend of Saint Brendan: A Comparative Study of the Latin and Anglo-Norman Versions.
Leiden, Netherlands: Koninklijke Brill NV, December 2008. 978-9-0041-6662-2, 9-0041-6662-9.

Moran, P F, ed. Nauigatio sancti Brendani abbatis [Voyage of Saint Brendan the Abbot]. Denis O’Donoghue, tr. excerpted from Brendaniana: St Brendan the Voyager in Story and Legend. Dublin: Browne & Nolan, 1893.
https://markjberry.blogs.com/StBrendan.pdf

Selmer, Carl, ed. Navigatio Sancti Brendani Abbatis, from Early Latin Manuscripts. Notre Dame, Indiana: University of Notre Dame Press, 1959. LCCN: 58-14184.

Turpin, William, ed. Navigatio sancti Brendani abbatis.
https://7d79bbc4-a-e92ee480-s-sites.googlegroups.com/a/swarthmore.edu/medieval-latin-summer-2013-the-gesta-francorum/home/latin-texts-of-the-gesta-francorum/Navigatio%20Sancti%20Brendani%20%28with%20commentary%29.pdf